Stable mist generation method and apparatus, the products and uses thereof

ABSTRACT

Disclosed is a series of methods and apparatuses for generating a stable water mist composed of water drops coated with a monomolecular film of long chain fatty alcohols whose carbon atoms are 16 and above. The methods include vaporizing and then condensing the alcohol to form particles of a suitable size for later intimately mixing with and thereby becoming a coating film upon generated drops of water. The water drops may be generated by means of a steam nozzle, spinning disc, or the agitation caused by an ultrasonic generator focused on the surface of a water bath or in the path of a water spray. The size of the drops can be controlled by the size of the generating equipment, temperature and quality of the steam or the intensity of the ultrasonic field. The alcohol particles may be held in solution with a volatile solvent which, after the spray mixing or emulsion of this solution and water drops, erupts causing the alcohol particle to burst out from the water drops to form a coating on the drop&#39;&#39;s surface. Insecticides, fertilizers, dyes and other materials may be added to the alcohol and water sprays so long as the additives have a neutral pH and do not cause imperfections in the alcohol film around the drop. The generated product of alcohol-coated minute water drops may be used to reduce the risk of frost damage to an orchard when the generated mist is directed through the orchard and thereby reduces the energy flux by reflecting and absorbing the heat energy which otherwise would escape into space as it is radiated from the earth and trees. The effectiveness of the mist for this purpose is enhanced when the water drops have a radius between 3 and 15 microns. In a similar manner the coated drops can form a floating lens system for reflecting and scattering infrared radiation. Another use of the generated product is to assist in the extinguishment of fires such as forest fires, by permitting a greater amount of water to be used for wetting the fuel of the fire and increasing the relative humidity closer to the fire since the coated water drops are more stable and can penetrate farther into the fire without having the moisture evaporated. Particularly good results occur when the radius of the water drops is between 50 and 100 microns. A dense opaque mist can be used to engulf an unruly mob reducing visibility to such a degree as to cause the mob to become disoriented and easily controlled.

United States Patent [72] Inventor ThomasY.Palmer Seattle, Wash. [21]Appl No. 687,046 [22] Filed Nov. 30, 1967 [45] Patented [73] AssigneeJune 15, 1971 The Boeing Company Seattle, Wash.

Continuation-impart of application Ser. No. 362,262, Apr. 24, 1964, nowabandoned.

[54] STABLE MIST GENERATION METHOD AND APPARATUS, THE PRODUCTS AND USESTHEREOF 14 Claims, 16 Drawing Figs.

[52] US. Cl ..47/2, 252/2, 252/300, 239/102, 239/223, 239/318 [51 Int.Cl G02b 5/24,

AOlg 13/06, C06d 3/00 252/305,

[50] Field of Search Primary Examiner- Robert E. BagwillAttorneyChristensen and Sanborn ABSTRACT: Disclosed is a series ofmethods and apparatuses for generating a stable water mist composed ofwater drops coated with a monomolecular film of long chain fattyalcohols whose carbon atoms are 16 and above. The methods includevaporizing and then condensing the alcohol to form particles ofasuitable size for later intimately mixing with and thereby becoming acoating film upon generated drops of water. The water drops may begenerated by means of a steam nozzle, spinning disc, or the agitationcaused by an ultrasonic generator focused on the surface of a water bathor in the path of a water spray. The size of the drops can be controlledby the size of the generating equipment, temperature and quality of thesteam or the intensity of the ultrasonic field. The alcohol particlesmay be held in solution with a volatile solvent which, after the spraymixing or emulsion of this solution and water drops, erupts causing thealcohol particle to burst out from the water drops to form a coating onthe drops surface. Insecticides, fertilizers, dyes and other materialsmay be added to the alcohol and water sprays so long as the additiveshave a neutral pH and do not cause imperfections in the alcohol filmaround the drop.

The generated product of alcohol-coated minute water drops may be usedto reduce the risk of frost damage to an orchard when the generated mistis directed through the orchard and thereby reduces the energy flux byreflecting and absorbing the heat energy which otherwise would escapeinto space as it is radiated from the earth and trees. The effectivenessof the mist for this purpose is enhanced when the water drops have aradius between Sand 15 microns. In a similar manner the coated drops canform a floating lens system for reflecting and scattering infraredradiation. Another use of the generated product is to assist in theextinguishment of fires such as forest fires, by permitting a greateramount of water to be used for wetting the fuel of the fire andincreasing the relative humidity closer to the fire since the coatedwater drops are more stable and can penetrate farther into the firewithout having the moisture evaporated. Particularly good results occurwhen the radius of the water drops is between 50 and 100 microns. Adense opaque mist can be used to engulf an unruly mob reducingvisibility to such a degree as to cause the mob to become disorientedand easily controlled.

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SHEET H []F 4 INVENTOR THOMAS K [34L MEI? A'ITORNEY STABLE MISTGENERATION METHOD AND APPARATUS, THE PRODUCTS AND USES THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part of my application entitled STABLE WATER FOG, Ser.No. 362,262, filed Apr. 24, 1964 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the invention This inventionrelates to the production of a stable water fog. More particularlystable water fogs are produced in this invention by coating the surfaceof a plurality of water drops with a film of alcohol which retards theevaporation and enhances the energy absorption and reflectioncharacteristics of the water mist.

2. Description of the Prior Art Over the years man has producedartificial mist in the 'form of sprays of wind-carried drops for manypurposes. in war time he has used chemicals and oils to generate a fogsuitable as ascreen to hide his troop movements from theenemys eyes. inthe production of food and particularly apples and other fruit, man hasgenerated oil fogs or smoke to ward off damaging frost from his foodproduction area. in addition, man has generated a water fog somewhatinadvertently in his effort to apply liquid water to a fire zone, sincepart of the water becomes heated from the fire and changes into a steamvapor before it has a chance to wet the fuel of the fire to help in itsextinguishment.

These uses by man of generated fog or smoke have several limitations anddisadvantages which have limited their desirability and broaderutilization. For the military man, smoke generation requires largequantities of hard-to-supply fog oil fuel to produce an effectivescreen. For the farmer, the noxious odors and the oily residue alongwiththe limitations in visibility in the treated area add to theinconvenience of previous attempts at making frost inhibiting fogs. Tothe tire fighter, the waste of limited supplies of water due to theevaporation of the water prior to its ability to wet the fuel, resultsin many fires going unimpeded untilthey reach ariver or other watersource, or become spent as they consume all the fuel in their paths.Thus, it is seen that it would be highly desirable to have available amist free from the detrimental characteristics of previously knowntoxic, corrosive, noxious and expensive manmade mists. in addition, itwould be desirable to have a more stable form of water available forfighting fires without high water losses due to evaporation. Further,the ability to use a frost retardant mist without obscuring thevisibility of those on the farm and those using nearbyroads would behighly desirable.

While it is an easy matter to suggest that water should be used in placeof the noxious, toxic fogoils previously used in generatedfrost-retarded smoke, water fogs have not been found practical due totheir inherent instability and rapid evaporation. It is known thatevaporation of water fields such as those used for the production ofrice hasbeen reduced by spraying a coating on the water surface. Thiscoating includes ethylene oxide derivatives from a reaction of normalaliphatic alcohols and hydrogenation of the oil or fat which containsglycerides glycerines of normal fatty acids with- 16 to 22 carbon atomsand two-thirds volume by weight-of'ethylene oxide. Such a process, whileeffective for submerged cr'ops, has no practical application forair-carried water mists since the mere 1 spraying of this coatingmaterial and water has avery poorefficiency for placing the coating onthe outside of the water drops to form an evaporation retarding filmaround-the drops.

Most of the coating material in such submerged-plant spraytreatments ismixed within the water drops of-the spray; Once the spray lands on thewater surface of the field, the coatingmaterial, having a specificgravity less than one, tends to float to the water surface to retardevaporation. in general-it has been difficult to develop a stableairborne water mist suitable for frost prevention and fire fighting;

It is therefore the principal object of this invention to produce aneconomical, stable water mist.

it is another object of the instant invention to produce a nontoxic fogof water drops coated by a monomolecular film of fatty alcohols havingl6 or more carbon atoms.

A stillfurther object of this invention is to produce'a stable water foghaving a drop size and selected film coating material which enhances itsability to absorb'and reflect heat energy for radiation shieldingpurposes.

Yet another object ofthe instant invention is to provide an inexpensive,stable, noncorrosive, nontoxic water mist which is useful for reducingfrost'damage to crops.

A still further object of the instant invention is to produce a heatinsulator using a stable water mist having the minimum amount of waterand a minimum amount of long chain fatty alcohol coating.

Still another object of the instant invention is to provide a simpleapparatus for producing. a stable water mist including means foradjusting-the size of the water drops making up the mist.

Still a further object of the'instant invention is to provide anapparatus for vaporizing and condensing the coating material to formoptimum size particles for coating the generated water drops.

Another object of the instant invention is to provide a method for thetreating a crop area with a stable water mist having drops of a selectedsize which enhances their ability to reflect and absorb heat energy fromthe earth providing an insulating effect which would otherwise requiremuch greater quantities of water, while at the same time having a dropsize which is large enough that the generated mist does not interferewith visibility in the area treated.

A still 'further object of the instant invention is to provide a methodfor combating forest and other fires including the use of a stable watermist which 'can be applied closer to the tire to wet the fuel thanuncoated water.

An additional object of the instant invention is to provide a stablewater mist which can be utilized as a medium for carrying fertilizer,insecticides and other treating chemicals to the bush and leaf portionsof plants while minimizing the amount of the treating material that willeither fall to the ground where it is of little value or spread undulyfar from the treated area with attendant toxic hazards.

SUMMARY'OF THE INVENTION The present invention relates to an improvedmethod and apparatus for generating a stable water mist and particularlyone which'includes water drops coated with a long-chain fatty alcoholfilm whose carbon atoms number 16 or more and mixtures thereof. One suchalcohol is n-l-iexadecanol, also called cetyl alcohol. The variousmethods disclosed include a method of generating water drops of anappropriate size for later coating and for generating the coatingmaterial in particle form of appropriate size for covering the waterdrops. Some apparatus includes chambers for vaporizing and condensingthefilm-forming material and intimately mixing it with the generated waterdrops. Other apparatus includes the use of ultrasonic means forgenerating an ultrasonic field which activates and enhances the mixingand coating action betweenthe water drops and coating material. Stillother apparatu's includes means for injecting steam against the coatingmaterial to vaporize it so that its condensed particles will be of anappropriate size for forming a monomolecular film on the surface ofwater drops generated by other steam nozzles.

The methods of reducing frost hazards in an orchard and of shielding anarea from radiation capitalize on the discovery of the enhanced Miescattering effect. Once the wavelength of the radiation is known acareful selection of shielding materials and their sizes will maximizetheir shielding effect while minimizing the shielding cost. Specificallywith reference to the orchard frost problem, it has been determined thatby selecting water in the form of a mist having a drop radius equal toor greater than the wavelength of the maximum energy flux or heatradiation generated from the earth and trees as they become coolerduring the night and early morning hours of the day and coating thesedrops with a long chain fatty alcohol, the drops are caused to act in anabsorbing and reflecting manner as if they were of a significantlygreater size. While this size of uncoated drops has a significantlyenhanced scattering cross section as compared to their physical crosssection, their stability and scattering cross section is furtherenhanced by the presence of the long chain fatty alcohols film on thedrops. Thus it is possible to provide a frost protection treatmentutilizing a small fraction of the water and coating material that wouldotherwise be required for the same absorbing and reflecting effects byutilizing the Mie scattering phenomenon to advantage in the selection ofcoating material and drop size for the treating medium.

Since the size of the drops forming the stable water fog can be rregulated by the various conditions and apparatus involved in theirgeneration, it is possible to develop a broad range of stable watermists useful for various purposes. As previously indicated, the size ofthe drops can be selected to take advantage of the efficiencyenhancement of Mie scattering effect. If a wetting action is desiredsuch as for fighting a fire, it is possible to generate drops of a largeradius which will, because of their coating, resist evaporation, butbecause of their mass will remain close to the ground until theirgenerated velocity has become spent, at which time they will fall to theground to wet the fuel making it more difficult to burn. If the stablemist is to be used as a carrier medium for applying an insecticide orfertilizer to the foliage of plants, the size of the water drops isselected so that the mist will not be so heavy as to carry theinsecticide and fertilizer to the ground but will allow it to float andbecome coated upon the foliage where it is desired.

In summary, this invention relates to the various means and methods forgenerating a broad range of stable water mists which have particularcharacteristics useful for a broad range of applications. This resultsin a nontoxic, cheaply generated product having very desirable usecharacteristics.

These and other features and advantages of the invention will becomemore clearly apparent from the following detailed description thereof,which is to be read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings FIG. 1 is a schematicdrawing illustrating the first embodiment of one means for generating astable water mist in accordance with the instant invention;

FIG. 2 is a schematic drawing illustrating a second embodiment of ameans suitable for generating a stable water mist in accordance with theinstant invention;

FIG. 3 is a schematic drawing illustrating a third embodiment of a meanssuitable for generating a stable water mist in accordance with theinstant invention;

FIG. 4 is a schematic drawing illustrating a fourth embodiment of ameans suitable for generating a stable water mist in accordance with theinstant invention;

FIG. 5 is a schematic drawing illustrating a fifth embodiment of asuitable means for generating a water mist in accordance with theinstant invention;

FIG. 6 is a schematic drawing illustrating a sixth embodiment of asuitable means for generating a stable water mist according to theteachings of the instant invention;

FIG. 7 is a schematic drawing illustrating a seventh embodiment of asuitable means for generating a stable water mist in accordance with theinstant invention;

FIG. 8 is a schematic drawing illustrating an eighth embodiment of asuitable means for generating a stable water mist in accordance with theinstant invention;

FIGS. 9a through 9d illustrate, in schematic form, the sequence ofdevelopment of a coating of a water drop such as produced by the eightembodiment in accordance with the teachings of the instant invention;

FIG. 10 is a schematic drawing illustrating the physical conditionsexisting during a typical frost danger period, and

FIG. 11 is a schematic drawing illustrating the treatment of the area ofFIG. 10 in accordance with one method of the instant invention forminimizing frost damage;

FIG. 12 is a schematic drawing illustrating the prior art practice ofutilizing water to fight a forest fire; and

FIG. 13 is a schematic representation of the forest fire area shown inFIG. 12 being treated with a stable water mist in accordance with themethod of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In general, this invention isconcerned with processes for, and products produced by coating waterdrops with long chain fatty alcohol to significantly retard their rateof evaporation. For certain uses, it is important that the mist producedhave an endurance or useful life during which the mist will serve as aneffective visual screen or thermal insulator. For practical purposes themethods and apparatus are adapted to use a minimum amount of alcohol forthe coating function.

Since long chain fatty alcohols are abundant and relatively inexpensive,their use for the coating material for the water drops produces aproduct which is relatively inexpensive and nontoxic. It has also beenfound that as the mist dissipates and the drops fall to the ground,there is no polluting problem with the residue, such as exist with othertreating and coating materials, since the fatty alcohols degenerate intosteric acids and other materials which are readily consumed by themicroorganisms generally existing in the crop of field areas.

The long chain fatty alcohols having 16 or more carbon atoms and endingwith an OH group are attracted by van der Waal forces of the OH groupsof the water to form a hydrogen bond between the alcohol molecule andthe water. One of the commonly used alcohols during the development ofthis invention is n-I-Iexadecanol, also known as cetyl alcohol. Thezigzag type of structure between the carbon and hydrogen atoms becomesoriented roughly perpendicular to the surface of the water drop so thatmany molecules of alcohol become packed together to form a monomolecularfilm which acts as a barrier preventing moisture from escaping throughthe tightlypacked zigzag structure of the filmforming molecules and alsoresisting additional moisture coming into the drop from outside. It hasbeen observed that the at attached chains of alcohol molecules have acertain attraction for one another so that they stand up rather close toone another to completely envelope the water droplet. This film reducesthe probability of escape of the water molecules from the droplet andthereby reduces the rate of evaporation of water from the droplet. Theterm used to describe the complete boundary or film layer of chains ofalcohol generally perpendicular to the surface around the fullcircumference of the water drops fully compressed monomolecular layer."Alcohol having less than 16 carbon atoms does not seem to be appropriatefor coating the water drop since its chain length is not long enough toproduce a significant reduction in the probability of escape of thewater molecules from the water drop.

As an example, the amount of cetyl alcohol required to form a layer overa water drop is based upon experimental results obtained for fiatsurface and is calculated as follows:

Let:

m,, mass of each drop r= drop radius p water density (1 in c.g.s. units)a,, surface area of drop M total mass of water N,, total number of waterdrops in Mass M,

A, total surface area of the drops in M,

Then:

d =1 gnL/(R YlFEIT' =11-3 X10 CH1. -/gal. Of water.

It has been found that eight grams of cetyl alcohol per acre of watersurface is sufficient to form a monomolecular layer over a lake underadverse conditions. This is equivalent to l gm/5.06 X l*cm of watersurface area.

Thus the amount of cetyl alcohol required to coat one gallon ofwater,divided into drops one micron in radius is:

5 :22.4 grn. /gal=49.4 lb./100 gal.

A more exact calculation is performed later.

A further advantage of the cetyl alcohol is that it is nontoxic for skincontact and ingestion, however, its effects when inhaled are not fullyknown. It has been the experience of test personnel that it is nontoxicwhen breathed in the concentrations used in experiments and in a fieldapplication the concentrations used would be about one thousand timesless.

In order to produce a stable water fog which will achieve these manydesirable objects, it is necessary that the ingredients be properlymixed to coat the water drop with the critical monomolecular layer offatty alcohol.

A typical apparatus with which there has been satisfactory results isillustrated by the FIG. 1, as the first embodiment 5, in which waterenters through inlet 11 and is pressurized and atomized into dropswithin the spray head 12. Then it is sprayed out of spray head 12 in theform of water drops 13. While the water is still in the form of dropsthe fatty alcohol is transformed into a vapor l4 and directed into thepath of the water spray so as to mix with and form a monomolecular filmon the surface of the water drops by condensing on the drop surface. Thefatty alcohol is vaporized by heating it to its evaporation point by anysuitable means such as by placing it in pan 16 on hot plate 17.

FIG. 2 shows the second embodiment for mixing the fatty alcohol andwater drops so as to coat the water drops by mixing a condensing jet ofsteam l8 and ajet of fatty alcohol 19 vaporized by a suitable means asin the burner 20. When this is done using cetyl alcohol, a densepersistent fog 21 is formed. Coating is believed to occur because thewater drops from the steam jet are relatively cool and offer the optimumcondensation sites for the cetyl alcohol vapor.

The stable water fog can be produced by forming a thin layer of alcoholupon the surface of water such as at 22 shown in the third embodimentillustrated in FIG. 3 wherein the surface of the water 22 is coated witha layer of alcohol and an ultrasonic generator 24 within the container23 of water is focused so that its output is concentrated on thewater-alcohol interface to generate a fine mist 25. In the process ofbreaking away from the topmost layer, the water drops entrain a coatingof alcohol. This material then spreads over the water drops, producingthe desired water mist having a thin layer of alcohol on the dropsmaking up the mist.

With reference now to the fourth embodiment 40 shown in FIG. 4, it isnoted that a fog 38 can be produced by directing a fine spray of waterdrops 31 from a spray head 32 toward a mixing area 35 where they meetand mix with a fine spray of fatty alcohol 33 as it is ejected fromnozzle 34. As the two jets 31 and 33 mix together they are passedthrough an ultrasonic field 37 which violently increases the agitationof the mixture so that the water drops and fatty alcohol impinge uponeach other resulting in the alcohol forming a monomolecular coating onthe surface of the water drops.

As a variation of this particular method, it could be considered thatthe mixing zone 35 permits the homogenization of the water and alcoholdrops prior to their passing through the ultrasonic field 36. In onetest using the fourth embodiment 40, the alcohol drops were sprayedhaving a size of approximately one micron in diameter and a ratio of onepart of fatty alcohol to one hundred parts of water. This then resultedin a range of drop sizes of l0O-200 microns just prior to passagethrough the ultrasonic field 37 which caused the breakup of the dropsinto a size of approximately one micron radius coated drops 38.

It has been found that the formation of stabilized water mists byincorporating homogenized coating materials consisting of long chainfatty alcohols containing 16 or more carbon atoms within the drop has alow efficiency in producing coated drops unless special precautionarymeasures are taken. This inefficiency arises from a set of probabilitieswhich when multiplied together give a low probability of success insuitably coating the water drop with a fully compressed monomolecularlayer. For purposes of explanation consider one drop of water withinwhich there is a particle of coating material. The required size of theemulsified particle may be computed as follows: It is known that a longchain fatty alcohol in a fully compressed monomolecular layer on a watersurface suitable for lowering evaporation rates will cover approximately20 square Angstroms (10 cm.*).

The surface area A, of the drop of radius r is:

The number of evaporation retarding molecules required to cover the dropis:

l6 n 20X 10 molecules/drop :2: gr. /molecule X molecules-drop chainalcohol.

The required radius r of the emulsified particle of cetyl alcohol is thecube root of the mass in grams M divided by the density p of the coatingparticle.

for the above cited example p,.=0.8 l 76 gr. cm. so that The ratio ofthe radius of the required homogenized particle to the radius of thewater drop to be coated is:

The ratio of the mass of the water drop M to the mass of cetyl alcoholrequired to give it a monomolecular fully compressed coating is:

For example, the ratio for cetyl alcohol is:

M,,/M=l .67 *lr. where r is in centimeters.

Another mist generator is the fifth embodiment 45 shown in FIG. 5.Particles 42 of the coating material are formed by impinging a spray ofdry st steam 43 onto the surface of the coating compound 44 in avaporizing chamber 46. This impingement produces particles 42 of thecorrect size for coating the desired size of the water drop produced atthe end of the nozzle 47, as will be described subsequentlyv A typicaltemperature of the dry steam 43 is 260 F. when the coating material isl--n hexadecanoic alcohol l6 carbon atoms) although this temperature maybe varied to produce different sized coating particles. instead of drysteam 43 other nonoxidizing gases, such as pressurized nitrogen orcarbon dioxide could be used to generate particles 42 of the correctsize for coating.

The mixture of coating particles 42 and steam 43 is introduced near therear end 48 of a chamber 50 at point 51 into the region 52 formed at oneend of the chamber 50. At the rear end of chamber 50 there is introducedthrough insert tube 54 a stream oflow quality steam 53. Typical valuesof pressure and temperature of water saturated steam 53 are p.s.i.g. and250 F. As the water saturated steam 53 is sprayed into the chamber 50 itflashes into steam vapor and water drops 55. While this evaporativeaction in region 52 prevents the disposition of the coating materialparticles 42 onto the surface of water drops 55. it does insure intimatemixing of particles 42 with the steam and water drops 55. ln addition,this spraying action and flow assist in the pumping of the particles ofcoating material 42 from the generator 45. Further along the chamber 50there is a venturi restriction formed at 57 to reduce the size of thechamber 50 forming an acceleration chamber 59. As the mixture of waterdrops 55, steam 53 and coating particles 42 pass through the venturireduction 57 into the smaller diameter acceleration chamber 59,particles 42 become accelerated reducing the pressure which, due to theresultant expansion of the steam vapor 53, tends to producesupersaturation. This tendency toward supersaturation causescondensation of the stream vapor 53 on the water drops 55 which havebeen carried along the steam. The condensing vapor flux toward the dropscarries the particles of coating material 42 which are also in thestream and intermittently mixed with the water drops 55 to the surfaceof the drops 55 in a Stefan flow until sufficient coating material 42has become collected on any one drop to coat it with a monomolecularfilm. The bulk of this formation takes place before the exit 60 of thenozzle 47 where the coated drops exhaust into the atmospheric region 61.The drops of water 55 which were initially so large as to haveinsufficient amounts of the coating material 42 on them are shrunk byevaporation after exiting into the atmospheric region 61 until themonomolecular layer of alcohol 42 is sufficiently compressed to becomeeffective in retarding evaporation at which time the rate of dropevaporation decreases by a factor of approximately one thousand. Thefinal water drop size inside the tube is adjustable from sizes as smallas one micron to one thousand microns or greater by varying thedimensions of the apparatus and the pressures and temperatures of theinjected water saturated steam 53. The final size of the coating waterdrop is controllable by varying the dimensions of the apparatus and thetemperature and flow rates of the dry steam 43 used to evaporate thecoating material 44. These parameters can thus be varied so as toutilize the coating material 44 and the water 55 to maximum efficiency.

it has also been ascertained that other materials 63 such asinsecticides, fertilizers, light and other radiation absorbing orreflecting materials such as carbon black, zinc sulfite and another suchmaterials such as carbon black, zinc sulflte and other such material canbe introduced into chamber 50 with saturated steam 53 from tube 54. Theresulting solution may have buffering material added to it if necessaryto maintain a neutral pH. The resulting mist, depending upon the size ofthe coated drops, will be useful for a wide variety of treatments.

One other apparatus for producing water drops having a desired radius isthat represented as the sixth embodiment 65 in FIG. 6. The methodpracticed by apparatus 65 is that of producing water drops 67 by using aspinning disc 68 with water 69 flowing up through the center axis of thedisc 68 and radially outwardly therefrom in the direction shown by thearrows. The coating material 70 flows from the upper feeder 71 throughthe conduits emanating downwardly at 72 onto the surface of water drop69.

The equation for the drop diameter d, from a spinning disc of diameterD, rotating with an angular velocity of w spraying a liquid from itsedge with a surface tension T, of a density P is:

where K is the constant 4.5.

The surface tension of water is about 70 dynes cm. The addition of amonomolecular long chain fatty alcohol layer to the water surfacereduces this value to that characteristic of the coating material suchthat the surface tension of the coated water is about 30 dynes cm.". lfadrop diameter of 20 microns or 2X10 cm is desired, for water density of1 gram cm, the above equation is used to solve for w and D as:

w D g 1.518X 10 cm. (rad. :secf

The coating mater'al 60 may be either solid or dissolved in a liquid. Asthe flow of ater continues outward it is spun off the sharp edge of thespinning disc 68.

As the drops come off the disc 68 they are equivalent to a cube of aheight h, with one side covered by the coating material. The volume of asphere is 4/31rr, which has a volume equivalent to that of a cube, h

Only one side of this cube is coated so that the coated area A is:

2/3 Ac h T The drop will shrink until this area covers the sphere with afully compressed monomolecular layer, i.e.,

solving for r R T2 W6 0.4507;

Thus the final radius of the fully coated drops will be approximatelyone-half the size of the drops as they come off the disc 68. Theaddition of greater amounts of coating material 70 to water can reducethis size reduction.

Alternatively, feed 71 may be left off and the fine particles of thecoating material 60 may be spread on the radially flowing water 69 by asifting device or other means.

Another suitable apparatus for generating stable fog 73 is shown as theseventh embodiment 75 illustrated in FIG. 7. The stable fog generator 75includes generating chamber 77 which may be filled at the lower end bysupply of clean water 78 through which is bubbled air 79 emanating froma spray outlet 80 positioned at the lower end of the chamber 77 andserviced by a suitable conduit 81 connecting the chamber 77 with thesuitable air supply 82. The bubbling of the air 79 through the water 78results in a saturated vapor, generally designated by the arrow 84,which flows upwardly through the generated chamber 77 toward its openend 85.

Connected by means of conduit 87 to the generator 77 is a vaporizingchamber 89 having an inlet spray head 91 connected to a suitable steamsupply 92 for impinging pressurized steam, shown as arrow 95, down uponthe coating material 97 which may be long chain fatty alcohol whosecarbon atoms number 16 or more or a mixture thereof. As the pressurizedsteam 95 impinges upon the coating material 97 it causes it to becomevaporized and mix with the pressurized steam flowing upwardly, as shownby arrow 99, out through the conduit 87 into the generating chamber 77.It exits from the conduit 87 through an expansion nozzle 100 to becomemixed with the saturated vapor 84.

As the two vapors of steam and coating material indicated generally byarrow 99 exit from expansion nozzle 100 there is a release of pressurecausing a condensation of the vapors into particles of coating material102 and liquid water drops 103. This jet stream of water drops 103,particles 102 and saturated vapor 84 pass through and around ring 105.Nozzles 107 are spaced around ring 105 to spray cold water generallyindicated by arrow 109 in such a manner as to mix the cold water withthe saturated air jet 84, steam formed water drops 103 and coatingmaterial 102 in particle from in the mixing region generally indicatedat 110 at the upper end 85 of the generating chamber 77 Cold water 109is supplied to ring 105 through a conventional conduit 112 connectingthe ring 105 with s suitable cold water supply 113. In the mixing region1 the excess of water vapor 103 produced by the steam 95, carrying thecoating material 102, and the water vapor 84 combine to cause the coldwater drops 109 to grow. In the growth process, the coating material 102is carried to the surface of the drops 103, 109 thereby producing waterdrops with a monomolecular coating of the coating material 102. Thesaturated air 84 flowing upward from the bottom of the chamber 77provides a positive flow creating a layer of floating air preventingimpingement of the coated drops 73 on the walls of the chamber 77.

The attraction of the particles 102 of coating material 97 and the waterdrops 109 may be further enhanced by applying an electrical potential 1between the cold water supply conduit 112 and the coating material jet99 as it passes through conduit 87 to oppositely charge the particles 97and drops 109 to increase their attraction. This applied electricalpotential has the additional benefit of increasing the dispersion of thewater sprays due to the repelling of particles electrically charged witha like charge. As the drops 109 grow the water vapor flows inwardlytoward the drop carrying the coating material 102 with it until the drophas grown to an appropriate radius coincident with the radius of thegathered coating material 102. This growth process will continue untilenough of the coating materials 102 have reached the surface of the drop109 to form a fully compressed monomolecular layer. At this point theflux of water vapor to increase the said of the drop will cease. Afterthis time, only a very small amount of coating material 102 will beadded if the drops are less than microns in radius, since the collisionefficiency between the particles 102 and drops 109 of this size andsmaller is below 0.1 percent.

It has also been found that simply spraying a mixture of water andhomogenized coating material such as long chain fatty alcohol whosecarbon atoms number 16 or more and mixtures thereof to produce a coatedfog is of extremely low efficiency. This low efficiency arises becauseof the low probability of the small particle of coating material beingat the surface of the drop of water as the drop is formed to a sizesuitable for the coating material to form a monomolecular film aroundit. If the coating material in particle form is in'the interior of thewater drop, it will be bonded to the water surrounding it by thehydrogen bond previously referred to. As the water drop shrinks to sucha size that the particle of coating material reaches the surface of thedrop it is necessary for the surface tension of the water to overcomethe attractive forces of the hydrogen bonding between the water of thedrop and the material before the coating material will be able to bepositioned outside of the drop. Since all of this activity of the dropshrinkage and of breaking of the surface tension of the water must takeplace within the lifetime of the drop, the efficiency of spraying amixture of water and homogenized coating material is extremely lowbecause the lifetime of an uncoated ten micronwater drop is less than 5seconds at'humidities less than percent.

Reference is now directed to FIGS. 8 and 9 for a disclosure of a methodwhich overcomes the inefficiency generally characteristic of spraying amixture of water and homogenized coating material to produce a coatedfog. The eighth embodiment of an apparatus for generating a coatedstable water mist is shown in schematic form in FIG. 8. Water 126 forthe mist comes from a suitable water supply 127 and is piped through asuitable conduit 128 to an homogenizer chamber 130. The coating material132, such as long chain fatty alcohol, whose carbon atoms number 16 ormore and mixtures thereof, is fed into a suitable mixing chamber 134where it is mixed with a material 135 which vaporizes at atmosphericpressure. It is preferred that the two materials 132 and 135 be mutuallysoluble. For example, a mixture of long chain fatty alcohol coatingmaterial 132 is mixed with a solvent 135, such as liquid butane formedunder pressure, so that the butane remains in liquid form. From themixing chamber 134 the resulting mixture 137 of the coating material 132and its solvent 135 is conveyed to the homogenizer where it is mixedwith the water 126 to produce a homogenized mixture of water 126 andmixture 137. This homogenized mixture is then jetted out through nozzle139 to the atmosphere to form the stable fog generally indicated at 140.If desired, an electrical potential 142 can be established on the exitside of nozzle 139 to assist in breaking up the spray into drops. Goodresults have been obtained when this electrical field is 960 volt/cm.

For purposes of understanding the formation of a coated stable waterdrop as a result of a utilization of the eighth em bodiment 125, asshown in FIG. 8, reference is now had to the sequence shown in FIGS. 9ato 9d. As shown in FIG. 9a the water drop 126 exits from the homogenizer130 through nozzle 139 it contains within itself the mixture 137 of thevolatile solvent and the coating particle 132. As water drop 126 'isreleased to the atmosphere through nozzle 139 it shrinks, as

shown in FIG. 9b, and the volatile material, such as the butane 135,starts to vaporize and expand until the drop 126 has a gas bubble formedin its surface such as shown in FIG. 9c. The coating particle 132 ispositioned to break out of the water drop 126 as in fact it does asshown in FIG. 9d where the coating material 132 has broken through thesurface of the water drop 126. At this instant a monomolecular coatingis rapidly formed around the water drop 126 thereby establishing thestable fog 140 as the vaporizing gas 135 escapes to the atmosphere.

It is therefore seen that by using a volatile solvent 135,- the coatingmaterial 132 has been able to blow itself out of the water drop 126 oncethe drop is ejected into the atmosphere. For example, if the size ofwater drops is to have a radius of 10 microns it would required acoating particle of long chain fatty alcohol, such as hexadecanol having16 carbon atoms of 1.5 microns in diameter. It is therefore seen that bypremixing the coating particles 132 with a volatile solvent 135 prior tohomogenizing and mixing water drops with the coating material, it ispossible to increase the efficiency of positioning the coating materialon the surface of the drops to produce a mist of stable water drops.

One of the uses for the stable water mist is that of preventing frostdamage to crops, such as apples and other fruit. To understand themanner in which the stable mist operates, it is necessary to understandthe various sources of heat and heat losses involved in an area such asorchard shown in FIGS. 10 and 11 where the stable mist would be applied.

Basically, a cooling effect results due to the fact thatduring nighttimeand early morning hours, heat energy from the suns radiation does notfall into the area of the orchard. Thus it can be considered that thelack of the sun's radiation provides one cooling effect of the orchardarea. A second cooling effect of the orchard area results from theconvection cooling which comes from cool air 152 as it is blown into theorchard area 150. Experience has shown that if the velocity of the airis much above miles per hour, frost will not form on the fruit because,either the wind turbulence will bring to the ground warmer upperatmosphere air or the temperature will be so low that freezing will takeplace. Therefore, when considering frost prevention the conditionsinclude the cooling effect of a slight breeze of air coming from coolerareas into the orchard area.

The earth in the orchard area 150 receives heat energy from the sunduring the day. It is considered a heat source during the night but theconduction of the heat from below to the soil surm is less than the lossby radiation of heat energy upwardly away from the earths surface asindicated by arrow 153. Another small source of heat energy in theorchard area is the trees 154 as they radiate heat energy, shown asarrow 155, during the night hours which they absorbed during the dayhours. In summary, the temperature decrease during the night hours isdue to the radiation of heat energy from the earth 153 up toward space,and the major cooling effects result from the cooler air 152 being blowninto the orchard area 150.

To understand the heat insulation or shielding function performed by thestable water mist 160 it is necessary that there is an understanding ofthe shielding effect of materials in general and the shielding effect ofspecific materials used in the stable mist in particular. The first ofthese effects to be considered is the effect of size of the drops. Thesecond could be considered the effect of selection of materials used forthe shield.

it has been found, and it is known, that when the ratio between theradius of the particles being used as a shield and the wavelength of theradiating energy is equal to one, there is a phenomenon called Miescattering which, depending upon the index of refraction and coefficientof absorption, may enhance the reflective and absorbing effectiveness ofthe shielding material significantly. To be more specific, if the radiusof a water drop used as a shielding material is equal to microns, it mayact in an absorbing, refracting and reflecting way as if it has 4 to 6times more cross-sectional area than the actual water drop used when itinteracts with electromagnetic radiation having a wavelength near to 10microns. This Mie scattering effect upon the apparent cross section toradiation is increased by another factor of 2 to 6 if the water drops of10 microns in radius are coated with a thin film of a long chain fattyalcohol layer the real part of whose index of refraction is greater thanthe square root of two.

The significance of the 10 micron water drop size and cross section Miescattering effect noted above becomes more clear when there is anunderstanding of the wavelength of the energy flux 153, i.e.., the flowof heat energy radiated from earth. When the energy flux is charted in agraph form against its wavelength, it is found that the major portion ofearth generated energy flux has a wavelength within the range of 3 tomicrons with its maximum portion having a wavelength of IO microns whenthe temperature is zero degrees Centigrade. Since this is thetemperature at which frost would otherwise occur, it is most appropriatethat water drops be formed with a radius of 10 microns, or at least inthe range of radius between 3 and 15 microns, to take advantage of theMie scattering effect.

To complete this discussion as to the shielding effect of the stablewater mist, it is necessary that there should be an understanding of theabsorption coefficient of the particular materials used in the stablewater mist. Again, with reference to a chart of the absorptioncoefficient, on one hand, and wavelength of the energy flux on theother, it is noted that for liquid water the curve peaks quite quicklyat a wavelength of about 9 microns to a maximum point of about 10microns, and then comes down partway to an effective range of up to l5microns. Cetyl alcohol, on the other hand, peaks up earlier and fallsoff with its peak curve starting at about 3 microns peaking up to itsmaximum point at about 7 microns, and dipping down to its leastsignificant point at about 1 1 microns, and then building back up again.Thus, it appears that a combination of liquid water and cetyl alcoholcovers quite nicely the heat energy wavelength as radiated from theearth in the orchard area 150.

The air temperature of the orchard area can be maintained above thefrost formation temperature in most frost danger situations if only arelatively small decrease in the heat loss results from the reflectingof such energy back to earth by means of the imposition of a cloud ofstable water mist over the orchard area.

When considering other materials which might also have long chain carbonhydrogen atoms terminating with an OH group, and suitable for reflectingand absorbing earth generated energy flux, it has been found that thealcohol molecule is quite effective when the carbon atoms number 16 ormore since such materials have an index of refraction above the squareroot of two and also have a molecular structure which forms good surfacecovering films.

What then are the characteristics of this film layer material which makeit suitable as a material for combining it with water drops for reducingthe frost danger in an orchard? Basically, long chain fatty alcohol isan abundant material. As the mist of water drops coated with the alcoholfilm finally disperse and evaporate, the residue is nontoxic. As amatter of fact, microorganisms such as are present in most all cropareas apparently like to eat the stearic acid formed in the residue, andin this way regardless of the number of repeated applications of themist to a single orchard area, the alcohol residue will not accumulatebecause of its consumption by the microorganisms in the orchard. Whilein its mist form, the drops are large enough so that they do notinterfere with the visibility of those operating on the fields ordriving on any roads adjacent to the fields. This, of course, is not thecase with previously used smoke generation systems which often leave asmudgy oil film in the area where the cloud has been formed. Inaddition, the alcohol-coated water drops are nontoxic.

The balance of the system is emphasized when attention is directed tothe fact that after the hexadecanol, that is 16 carbon atom long chainfatty alcohol, has been first vaporized and then condensed, thecondensation product formed is a particle of bunched hexadecanol longchain molecules. The cross section diameter of this particle isapproximately 1.7 microns. This is the exact size of hexadecanolparticles required to coat a 10 micron radius water drop. Thus, it isseen that the condensation of hexadecanol results in the formation of ahexadecanol particle formed from the same number of hexadecanolmolecules as is necessary to coat a 10 micron radius water drop. Thissize water drop, as mentioned before, is the one which gives the optimumreflective and absorptive effect for the type of energy flux radiated bythe earth.

in operation, as shown in FIG. 11, a series of stable mist generators,such as embodiment 45, are placed upwind of the orchard area to betreated and the generation process as previously described is initiated.The mist that forms is approximately 60 feet wide and 30 feet deep andis continuously generated as it moves along across the orchard beingcarried by the wind 152. It has been found that the normal life of themist is approximately one hour at 0 Centigrade. It has also been foundthat it requires about 10 pounds of water per acre and 0.01 pounds ofhexadecanol per acre for a 3 hour run at an initial temperature of 0Centigrade.

As illustrated in FIG. 11, the heat energy introduced into the mist bymeans of the steam assists in overcoming the cooling effect cause by thewind convection cooling of lower temperature air 152. This mist 160itself as it covers the ground surface also acts as a retardant shieldas indicated by arrows 162, of the heat energy or energy flux to reducethe net heat loss, indicated by arrow 163, as it is radiated towardspace from the earth and from the trees themselves. The size TABLE IJLIFETIMES AND FALL DISTANCES FOR A 10 VICRON WATER DROP COATED WITHHEXADECANOL A'I C. WITH AN INITIAL VELOCITY OF 1.25 CMJSEC.

Relative Vertical humidity, Lifetime, distance percent seconds meters504. 8 2. 12 560. 9 2. 35 631. 0 2. 65 7' Z 3. 03 841. 4 3. 53 l, 009. 74. 24 1, 262 5. 30 1, 682 7. 06 2, 524 10. 7 5, 048 21. 2 I 096 42. 6

While the description of a stable fog has been related to its use inreducing frost hazard to an orchard area, the stable mist has been usedfor other crops. For example, a test run using an experimental unit ofthe mist generator was begun when the temperature over a blueberry bogwas dropping dangerously low. Once the stable fog had been generatedwith the cloud at about bush top level, the temperature held F. higherthan the temperature outside of the fog blanket thereby saving theblueberries from low temperature damage. In another test in an area withvery little wind, the temperatures in the zone covered by the artificialfog rose under the fog from 30 F. to 36 F. after 20 minutes under thestable fog. Other uses where the radiation of energy flux having awavelength from 3 to microns is to be reflected and absorbed couldutilize the stabil ized mist as herein described.

The foregoing treatment description for reducing frost damage in anorchard is merely representative of one practical utilization of theelectromagnetic radiation scattering and reflecting properties of thestable mist of the instant invention. A very broad field of applicationsof these properties should become more apparent as more experience isgained through the use of the stable mist in shielding areas fromvarious sources of radiation. Basically it can be considered that theoperator can generate a stable mist with customized drop size, coatingmaterial and possibly additives to establish a floating shielding lenssystem for scattering, reflecting and absorbing radiation. Dependingupon the wavelength of the radiation, the properties of the mist can bevaried to optimize the effects of the shield.

Scattering and absorption of electromagnetic radiation effects withmicrowave radiation have been explained in the technical literature forsingle particles of isotropic and nonisotropic materials. The design ofcoated water particles for optimizing a radiation shield mist can bemathematically obtained. Quantitive estimates of absorption andscattering for coated water particles can be made from geometric opticsas follows:

Since the index of refraction, n, of cetyl alcohol is greater than thatof water (1.428 as compared to 1.333), the critical angle is smaller(44.5 as compared to 48.6). Thus an incident light beam will penetrateover approximately 15 percent less of the water drops area if the dropis coated with cetyl alcohol. Inside the drop, however. the presence ofthe multiple layers enhances absorption and reflection. For example, fornormal incidence the reflecting power R is:

(n 1) R (n-- 1 For air to water, R=0.0625; for air to cetyl alcohol,R=0.0900; and for air to water coated with cetyl alcohol R=0.00427. Withthe radiation encountering all of these materials in one coated drop thecombined effect is a substantial attenuation of the radiation.Transmission of radiation through a drop (at normal incidence neglectingmultiple reflections) is then 87.8 percent for water drops and 81.9percent for coated water drops.

To insure that the radiation striking the coated drop will be absorbedor reflexed back toward the source of radiation the coating materialmust have an index of refraction within the range between the squareroot of two (1.414) and two. Below this range, the radiation is focusedbeyond the drop in a direction away from the source. Above this range,the radiation may be focused within the drop but not to the reflectingback surface of the drop. Within the range the radiation is focused atthe back reflecting surface of the drop causing it to follow a path backtoward its source.

Furthermore, in order to increase radiation absorption and reflectionwithin the coated drops certain additives can be incorporated into thedrops. Since the medium through which the radiation passes within thedrops is water the index of refraction for the additives is within therange between 1.333X2 or 1.885 to 1.33X 2 or 2.667. Such additives canbe soluble or in soluble in water or even in particulate form as long asthe drop has or is buffered to a neutral pH. Since they are goodradiation absorbers and are also nontoxic, carbon blaclc and zincsulfide can be used as additives for the coated drops to enhance theirability to absorb and reflect radiation.

One use for such a radiation shield, beyond that described for orchardsto reduce losses of earth generated infrared radiation, is as a thermalradiation shield around a defense site. A missile launching station orpopulation center could have an additional margin of protection from anuclear explosion if a mist could be generated in the path of thethermal radiation to reflect, scatter and absorb some of the harmfulelectromagnetic radiation before it reaches the site or populationcenter. In essence the generated mist forms a temporary but stablefloating lens system for scattering, reflecting and absorbing radiation.The size of the drops and selection of drop and coating materials takesadvantage of the cross section enhancement Mie scattering effect. Inaddition the index of refraction for the long chain fatty alcoholcoating materials with 16 carbon atoms or more is between the squareroot of two and two yielding excellent reflecting, scattering andabsorption results by focusing the radiation into the interior backsurface of the drop. Further it has been found that with such coateddrops there is a skin effect which generates standing waves for sprayingthe radiation back to its source.

Since the fog generating equipment described herein carries out theconcept of forming a monomolecular evaporation regarding coating aboutthe individual water drops, its operation increases substantially theuseful life of such drops opening up many uses for the generatedproduct. One such use is that of combating forest fires. As shown inFIG. 12 a schematic representation of a forest 170 is depicted withtrees 172 engulfed in flames 174 as the area is being subjected toconventionally applied liquid water 176 directed toward the fire 174 bymeans of water nozzle 178. Due to the heat energy and local airturbulence around the fire a good portion of the water 176 directedtoward the fire is evaporated and has no effect on the fire. The onlyway that the fire becomes controlled is by soaking the potential fuel ofthe fire so that it cannot be raised to the kindling point or otherwiseby denying oxygen to the fire area.

FIG. 13 illustrates the same fire zone 170 with the trees 172 engulfedin flames 174 as it is treated by the improved technique possible as aresult of the instant invention. For this treatment a fog generator orseries of fog generators such as the fourth embodiment generator 45 isplaced upwind of the fire to generate a stable mist of water dropsgenerally indicated at 179.

It has been found that for purposes of wetting the potential fuel forthe fire, the drop size of the water drops should be held in the rangebetween about 50 and microns. Since the individual drops are coated withthe monomolecular long chain fatty alcohol film having 16 or more carbonatoms and mixtures thereof, the drops are more stable and less likely toevaporate before a good portion of the generated water drops reachessome part of the fuel close to the fire zone. Thus, the fire is moreeasily controlled with a less amount of water using the stable watermist of the instant invention than would be needed if ordinary waterwere used because the stable film will permit more of the fuel wettingwater to get closer to the fire zone before part of it becomeevaporated.

if the treatment requires the addition of additives such as fertilizeror insecticides which are desired to be coated on the leaves of cropsrather than on the ground, it is possible to select a drop size whichwill provide the best floating medium for carrying the additives to theleaves. if the additives are to soak the area such as in the case of thefire fighting application the drop size can be increased such that theywill drop to the ground after being carried by the wind to theapplication area. Other additives such as dyes for coloring a screen andinhibiting visibility can be used with the stable mist generated inaccordance with the instant invention. Whenever additives are consideredfor addition to the stable mist of the instant invention, it isnecessary that the additives be buffered to a neutral pH so that theywill not break down the coating function of the long chain fatty alcoholmonomolecular film. It is also necessary that the additives should notbe of a nature such as ethyl alcohol which will dilute the fatty alcoholand cause holes in the film such that the evaporation retarding filmwill not be fully formed and the drops will not have the extended lifeotherwise provided by the monomolecular long chain fatty alcohol film.

Another example of the variety of uses for a stable water mist is thatof riot control. One test demonstrated that a mist could he formed inless than a minute which filled a large room with a stable drops havinga size between 0.5 microns to 5 microns. This mist so engulfed theoccupants of the room that they became completely disoriented. Drops inthis range are opaque to such an extent that the room's occupants couldnot see their hands more than 6 inches from their faces. The mistremained effective for nearly one half hour even after doors were openedto increase air circulation in the room. With this use in mind, prisoncells and common areas could be equipped with nozzles connected to amist generator. Once a riot started it could be quickly controlled for along enough period to bring in adequate force without inflicting injuryupon the occupants of the areas so treated.

It is therefore seen that depending upon the particular characteristicsdesired, a wide range of improved treatments is available by utilizingthe stable water mist concept as described herein.

What I claim is:

1. in the process of protecting open-air objects such as foliage againstfrost, fire, or the like by forming an artificial fog thereabout, thesteps of generating a mass of vaporous droplets consisting essentiallyof water, at a point adjacent the foliage, causing relative motionbetween the mass of droplets and a mass of water insoluble particlesconsisting essentially of a monohydric long chain fatty alcohol having16 or more carbon atoms therein, so as to impinge one mass on the otherand coat the outside surfaces of the water droplets with the alcohol,and discharging the mass of droplets into the atmosphere about thefoliage so that the coated droplets form the required fog.

2. The method according to claim 1 wherein the mass of droplets isdischarged into the atmosphere as a spray, and the droplets are coatedby releasing vaporous alcohol particles into the atmosphere across thepath of the spray.

3. The method according to claim 2 wherein the alcohol particles arereleased into the atmosphere as a spray which is directed across thepath of the water spray.

4. The method according to claim 3 wherein the intersecting water andalcohol sprays are passed through an ultrasonic field.

5. The method according to claim 1 wherein the mass of water droplets isdischarged into the atmosphere from a container, and the droplets arecoated by releasing vaporous alcohol particles into the container acrosstheir path of discharge.

6. The method according to claim 5 wherein the vaporous alcoholparticles are infused under pressure with a gaseous water insolublesolvent therefor, before being intermixed with the droplets in thecontainer.

7. The method according to claim 5 wherein the vaporous alcoholparticles are generated by spraying steam onto the alcohol.

8. The method according to claim 7 wherein the alcohol is in a solidstate when it is bombarded by the steam.

9. The method according to claim 7 wherein the particles are generatedin an enclosure and released through an expansion nozzle.

10. The method according to claim 5 wherein the mass of water dropletsis generated by aerating a body of water in the container.

11. The method according to claim 5 wherein the water droplets and thevaporous alcohol particles are oppositely electrostatically charged toenhance the attraction therebetween.

12. The method according to claim 5 wherein the droplets are dischargedthrough a venturi nozzle.

13. The method according to claim 1 wherein the mass of water dropletsis discharged into the atmosphere from a container, and the droplets arecoated by interposing a film of liquid alcohol particles in thecontainer across their path of discharge.

14. The method according to claim 13 wherein the mass of water dropletsis generated by ultrasonically dispersing a body of water in thecontainer.

1. In the process of protecting open-air objects such as foliage againstfrost, fire, or the like by forming an artificial fog thereabout, thesteps of generating a mass of vaporous droplets consisting essentiallyof water, at a point adjacent the foliage, causing relative motionbetween the mass of droplets and a mass of water insoluble particlesconsisting essentially of a monohydric long chain fatty alcohol having16 or more carbon atoms therein, so as to impinge one mass on the otherand coat the outside surfaces of the water droplets with the alcohol,and discharging the mass of droplets into the atmosphere about thefoliage so that the coated droplets form the required fog.
 2. The methodaccording to claim 1 wherein the mass of droplets is discharged into theatmosphere as a spray, and the droplets are coated by releasing vaporousalcohol particles into the atmosphere across the path of the spray. 3.The method according to claim 2 wherein the alcohol particles arereleased into the atmosphere as a spray which is directed across thepath of the water spray.
 4. The method according to claim 3 wherein theintersecting water and alcohol sprays are passed through an ultrasonicfield.
 5. The method according to claim 1 wherein the mass of waterdroplets is discharged into the atmosphere from a container, and thedroplets are coated by releasing vaporous alcohol particles into thecontainer across their path of discharge.
 6. The method according toclaim 5 wherein the vaporous alcohol particles are infused underpressure with a gaseous water insoluble solvent therefor, before beingintermixed with the droplets in the container.
 7. The method accordingto claim 5 wherein the vaporous alcohol particles are generated byspraying steam onto the alcohol.
 8. The method according to claim 7wherein the alcohol is in a solid state when it is bombarded by thesteam.
 9. The method according to claim 7 wherein the particles aregenerated in an enclosure and released through an expansion nozzle. 10.The method according to claim 5 wherein the mass of water droplets isgenerated by aerating a body of water in the container.
 11. The methodaccording to claim 5 wherein the water droplets and the vaporous alcoholparticles are oppositely electrostatically charged to enhance theattraction therebetween.
 12. The method according to claiM 5 wherein thedroplets are discharged through a venturi nozzle.
 13. The methodaccording to claim 1 wherein the mass of water droplets is dischargedinto the atmosphere from a container, and the droplets are coated byinterposing a film of liquid alcohol particles in the container acrosstheir path of discharge.
 14. The method according to claim 13 whereinthe mass of water droplets is generated by ultrasonically dispersing abody of water in the container.